This invention relates generally to the field of measurement engineering and to the machine-working of workpieces to produce cylindrically-shaped workpieces; more particularly to the measurement of deviations of shape or form of nominally cylindrical, including conical and barrel-shaped, workpieces; and still more particularly to the machine-working or cutting of cylindrically-shaped workpieces from blanks having a longitudinal central axis that is unsymmetrical and/or positionally unstable with respect to a machining or cutting tool.
Precision cylindrical workpieces, such as shafts and axles, are extensively used in present-day machines and mechanisms. Very often, deviations from roundness of these cylindrical parts greatly affects the effectiveness and efficiency of the machines incorporating such workpieces. For example, deviations from from roundness of journals causes vibration, noise, heating and other adverse phenomena in ball and roller bearings, and so greatly shortens their useful life. Roundness is equally important for such elements, as crankshaft necks, piston pins, electric motor commutators, etc.
Existing methods and devices are only capable of overcoming the problem caused by deviations from roundness in machined workpieces, and are capable of testing for such deviations in relatively small workpieces (generally, those that are up to 400 mm in diameter and up to 500 mm in length), while the workpiece is out of a machine tool that is used to cut or otherwise shape the workpiece into a cylindrically-shaped object; and only while the workpiece or object being measured is stationary, using a stationary roundness tester.
One known device for measuring the roundness of a workpiece while it is out of the cutting tool or other machine used to impart the rounded shape into a blank is disclosed in Russian Patent No. SU 1,623,573, which issued Feb. 24, 1987. The device disclosed there includes a frame mounted on four damped bearings for vibration elimination. A mount, having a turntable for a workpiece to be measured, is attached to a frame on which there are secondary shock dampers. A sensor with a fixing pen, or measuring stylus, which tracks and interacts with a surface of the workpiece, is fitted on a motor-driven sliding member. The pen or stylus is utilized for measuring various parameters relating to the deviation of certain dimensions of the workpiece, and the surface structure of the workpiece, from ideal roundness and straightness, as applicable. The pen or stylus tip is capable of movement in any direction within a rectangular-shaped work area.
The device of this reference, however, has a number of drawbacks, specifically:
xe2x80x94it is technically complex, and is not completely protected against vibration, which affects the accuracy of its measurements; and
xe2x80x94the device is not suitable for use in measuring large workpieces, such as calenders or forming rolls, in which deviations from roundness may have an effect on the quality of paper, foil, rolled products, etc. produced on machines incorporating such workpieces.
A device and method for measuring deviations from roundness of an object is also disclosed in U.S. Pat. No. 3,942,253, which issued May 3, 1974. The device of that reference includes a linear displacement-sensing element, radial locating support members, which are made as multi-stepped, self-adapting rocking levers that are symmetrically positioned with respect to the linear displacement-sensing element. When a workpiece rotates without axial movement, a measuring gauge of the device measures the deviation from roundness of the workpiece""s cross-sectional profile.
This device of this reference also has a major limitation in that it can measure only one parameter of a cylindrical piece, namely the deviation from roundness. Measurement of only the deviation does not, however, give a full indication of the workpiece""s shape, and so does not enable a complete determination of the precision of machining of a cylindrical workpiece, since other shape-related parameters along the axial length of the workpiece cannot be properly measured.
Precision machining of long cylindrical workpieces creates a number of problems because of the presence of steadying elements or rests positioned along the length of the workpiece or object, which are used for holding the workpiece steady and in place on a machining tool used to cut a cylindrically-shaped object from a workpiece blank . The presence of such steadying rests prevents precise positioning of the longitudinal axis of rotation of the workpiece with respect to the cutting tool. In fact, the presence of such steadying rests often leads to a transfer of deviations from roundness from a reference object to the machined object.
A steadying rest of the type mentioned above, is disclosed in Russian Patent No.
SU N2 1,660,929, which issued May 3, 1989. The steadying rest of that reference includes a body having a piston with a piston rod linked through a moving chain with an inverted V-type and a presser jaws. The moving chain is made as a rigid bar with stop members and an additional rod aligned with the main rod and designed to interact with the presser jaw through introduced spring-loaded rod. The apparatus functions as follows: the prismatic jaw is driven to the reference piece and positioned to grasp tightly the neck, then fixed so. After adjustment, the piece is placed in the machine tool and the piston is moved to press the inverted V-type jaw to the piece.
Simultaneously the secondary rod moves the piston, which presses the presser jaw to the piece by rotating it. After completion of machining, the piston is moved to the right, the presser and the prismatic jaws are taken off the piece.
The device of this reference has a number of shortcomings, which cause deviations of form to be transferred from the reference surface to the workpiece being machined. In addition, the steadying rest of this reference does not allow for the machining of large, heavy pieces, thereby severely limiting its use.
Another steadying rest, with self-adjusting supports, is disclosed in the journal Stanki i instrument, 1976, No. 7, at p. 22-23. In the body of the steadying rest disclosed there, there are two self-adjusting inverted V-blocks movable in a radial direction. The workpiece is pressed to them with its external (datum) surface through a spring-loaded stop. Additionally, there is a secondary support that is a pad made from a fluoroplastic material in the steadying rest""s body, which functions to partially counterbalance the weight of the workpiece.
A limitation of this device is the spring-loaded horizontal stop, which presses the workpiece against self-adjusting bearings. If the machining datum surface has deviations from roundness, then this stop follows these deviations when the workpiece rotates, the stop must move for distances equal to datum surface""s deviations from roundness. A still further limitation of this device is that it also does not allow for machining of large, heavy workpieces, thereby severely limiting its use.
Still another device for the machining of surfaces of revolution onto a workpiece having a longitudinal central axis that is unsymmetrical and/or unstable with respect to the machining tool during the machining is disclosed in Russian Patent No. RU N2 2,111,089, which issued Feb. 20, 1996.
Corrections to the workpiece shape are made by placing the cutting tool within the angle of supporting element shoes. The shoes and the tool are mounted on a single bracket, which is capable of rocking movement in a plane perpendicular to the workpiece""s axis of rotation.
The device of this reference has a limitation in that the force of pressing the shoes and the tool against the workpiece surface depends on the elastic strain of a spring, which is not constant. This circumstance has a negative effect on the machining accuracy. Furthermore, the device does not allow for a run-out greater than 10 mm, as the bracket with the shoes cannot track such large displacements of the workpiece, and the device will not work in such situations.
The foregoing analysis of the prior art is supported by the results obtained from existing devices. These results are known to the person skilled in the art of precision shaft machining and support the conclusion that prior to the apparatus and method of the present invention, there has been no highly effective device or method, which allows for:
xe2x80x94precision measurement in detail of separate geometrical parameters of the surfaces of various generally cylindrical shapes, such parameters including: longitudinal cross section profile (taper, barreling, etc.); deviations from straightness or linearity of a central longitudinal axis of a workpiece; run-out of the surface of a workpiece with respect to a of reference surface, such as in bearing journals, where such deviations need to be measured in order to obtain precision machining of cylindrical workpieces; and
xe2x80x94precision machining of cylindrical workpieces having a longitudinal central axis of rotation that is unsymmetrical and/or unstable with respect to the machining tool;
both of which are achieved by the apparatus and method of the present invention.
Accordingly, some of the limitations of the prior art that are overcome by the apparatus of the present invention, and some of the advantages of the apparatus of the present invention over the prior art, are:
xe2x80x94the apparatus of the present invention provides more universal device and method than was previously known by enabling a wider range of measured deviations of form of cylindrical pieces;
xe2x80x94more accurate measurement of deviations of form of cylindrical workpieces and more precise machining of cylindrical workpieces having a longitudinal central axis of rotation that is unsymmetrical and/or unstable with respect to a cutting or other machining tool is possible with the apparatus and method of the present invention;
xe2x80x94measurement of deviations of form of, and the machining of large, heavy cylindrical pieces is made possible through the apparatus and method of the present invention.
The problems and limitations of the prior art are overcome by the apparatus and method of the present invention in the following ways:
xe2x80x94the apparatus of the present invention provides relative stabilization of the position of the axis of a rotating workpiece by use of multi-stepped, self-adjusting inverted V-type supports;
xe2x80x94the apparatus and method of the present invention allow measurement of the following deviations of form of a workpiece:
xe2x80x94deviation in the roundness of a cross sectional profile of the workpiecexe2x80x94xcex941,
xe2x80x94deviations in the shape of the longitudinal section of the workpiecexe2x80x94xcex942,
xe2x80x94deviations in the straightness of a central axis through the workpiecexe2x80x94xcex943, and
xe2x80x94deviations in the radial run-out from the center of a cross sectional profile of the workpiece (where the center is the center of an average, xe2x80x9cleast squaresxe2x80x9d circle)xe2x80x94xcex944.
According to the method of the present invention, deviations in the roundness of a cross section is measured using a first measuring sensor of a gauge, with a measuring tip which contacts the surface of the workpiece.
A second measuring sensor, which is fitted on an arm of a mount of the apparatus, and which also has a measuring tip that contacts the workpiece, is used to measure deviation in the radial run-out of the profile from the center of an average, xe2x80x9cleast squaresxe2x80x9d fitted circle, while the workpiece is being rotated. The first sensor measures the deviations from roundness of the piece cross sectional profile, and the second sensor measures radial run-out of the center of the profile, based on the center of an average, xe2x80x9cleast squaresxe2x80x9d circle. In cases where there is axial feeding of the gauge mount along the axis of the rotating workpiece, the first sensor measures the deviation from roundness of different cross sections and deviation of the average radius along the workpiece, and the second sensor measures the radial run-out of the corresponding cross section profile centers (centers of average circles). The actual workpiece central longitudinal axis is a line connecting the centers of adjacent ones of its cross sectional profiles. These measurements enable a determination to be made as to the workpiece""s cross sectional profile shape, its longitudinal section profile, and the straightness of its central, longitudinal central axis.
For measurement of deviaton from roundness and axial misalignment of the workpiece profile with respect to a datum profile, a bracket is fitted in the gauge body with a third measuring sensor, also having a tip which contacts the surface to be measured.
The device for measuring shape deviations of a workpiece having at least certain cylindrical properties, according to the present invention, includes a rider-type roundness tester with multi-stepped self-adapting support elements and a first measuring sensor fitted on the body. The device is suspended on a vertical mount, which is capable of axial movement along the workpiece. A measuring unit is fitted on the above mount, the measuring unit consisting of an arm with the second measuring sensor on the one end. The other end of the arm is fixed to the vertical mount, such that the second sensor""s tip contacts the roundness tester body.
In an alternative embodiment, the first sensor functions in the same manner as the second sensor in the previous embodiment. In this alternative embodiment, the measuring unit is replaced with an arm having one end fixed to the vertical mount and having a flat area on the other end. The first sensor""s tip contacts the flat area of the arm.
In order to measure deviations from roundness and axial misalignment of a workpiece profile with respect to a reference, a third measuring sensor on a bracket is added to the device. The bracket is fitted on the roundness tester body, a tip of the third sensor contacts with the surface of the workpiece being measured.
One advantage of the apparatus of the present invention is the ability to perform workpiece form measurements without taking the piece off the grinding or turning machine. Workpiece machining is performed on the same machine using specially designed follower and correcting steadying rests that are based on multi-stepped, self-adapting support elements.
A correcting steadying rest includes a body having main, multi-stepped, self-adapting, inverted V-type support elements and at least one secondary support for weight compensation. The steadying rest has a sliding member and a rocking yoke that is capable of vertical movement and rotation. The main support elements are hinged to the ends of the yoke. The secondary support is a similar inverted V-block on the sliding member. The sliding member is positioned at an angle to the vertical and is capable of linear movement within the steadying rest""s body. The main support elements of the steadying are fitted on the rocking yoke so that the angle between radii passing through the workpiece""s center of rotation and the axes of the main support elements is from about 50 to about 130 degrees. Each of the main support elements is so positioned that the angle between the radii passing through the piece""s center of rotation, the center of the main support elements, and the point of contact of an inverted V-block with the workpiece is from about 10 to about 40 degrees. The sliding member is positioned at an angle of from about 5 to about 20 degrees between the vertical and a line passing through the center of rotation of the workpiece and the axis of the secondary supports. The rocking yoke lever has arms of equal length that are capable of movement along the body of the workpiece.
A correcting follower rest includes a body with multi-stepped, self-adapting, inverted V-type support elements and a cutting tool capable of rocking in the plane perpendicular to the piece""s axis of rotation.
The body of the correcting follower is made in the shape of a yoke and is fitted on a lever that in turn is capable of turning on a mount that is fixed to the machine support. The cutting tool is capable of displacement along the body within an angle of from about 0 to about 180 degrees with respect to the axis of symmetry of support elements. The body is mount on a lever and is capable of displacement within the angle 60 degrees in respect of the vertical. The support elements and the cutting tool are positioned in parallel planes perpendicular to the axis of rotation of the workpiece. The inverted V-type support elements may be singlexe2x80x94or multi-stepped. Each support element includes a rocking lever having an opposed pair of end, with shoes hinged to each end.
Typically, the tool for cutting the workpiece from a blank is a lathe cutter or a grinding wheel.
The above-described structures of devices according to the present invention are based on stabilizing the position of an object (for example, a measuring sensor or cutting tool) with respect to the main longitudinal central axis of a rotating workpiece by use of multi-stepped, self-adapting, inverted V-type support elements. The angles between the support elements and the workpiece are determined by a specially developed mathematical expression. Devices built in accordance with this expression have many points of contact with the rotating workpiece and many degrees of freedom. The result is high-precision position stabilization of a measuring sensor or a cutting tool with respect to the workpiece axis, irrespective of any deviations from roundness in the shape of the workpiece""s surface.